/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.contrib.streaming.state.iterator;

import org.apache.flink.contrib.streaming.state.RocksIteratorWrapper;
import org.apache.flink.runtime.state.StateSnapshotTransformer;

import org.rocksdb.RocksIterator;

import javax.annotation.Nonnull;

/**
 * Wrapper around {@link RocksIterator} that applies a given {@link StateSnapshotTransformer} to the elements
 * during the iteration.
 */
public class RocksTransformingIteratorWrapper extends RocksIteratorWrapper {

	@Nonnull
	private final StateSnapshotTransformer<byte[]> stateSnapshotTransformer;
	private byte[] current;

	public RocksTransformingIteratorWrapper(
		@Nonnull RocksIterator iterator,
		@Nonnull StateSnapshotTransformer<byte[]> stateSnapshotTransformer) {
		super(iterator);
		this.stateSnapshotTransformer = stateSnapshotTransformer;
	}

	@Override
	public void seekToFirst() {
		super.seekToFirst();
		filterOrTransform(super::next);
	}

	@Override
	public void seekToLast() {
		super.seekToLast();
		filterOrTransform(super::prev);
	}

	@Override
	public void next() {
		super.next();
		filterOrTransform(super::next);
	}

	@Override
	public void prev() {
		super.prev();
		filterOrTransform(super::prev);
	}

	private void filterOrTransform(@Nonnull Runnable advance) {
		while (isValid() && (current = stateSnapshotTransformer.filterOrTransform(super.value())) == null) {
			advance.run();
		}
	}

	@Override
	public byte[] value() {
		if (!isValid()) {
			throw new IllegalStateException("value() method cannot be called if isValid() is false");
		}
		return current;
	}
}
